Kaposi's sarcoma- and B cell lymphoma-associated human herpesvirus 8 (HHV-8) specifies particular proteins that are believed to contribute to angioproliferative and malignant pathogenesis. Key among these is the interleukin-6 homologue, vIL-6, which via its signal transducing properties promotes angiogenesis, cell proliferation and cell survival. The expression of vIL-6 is maximal during lytic, productive replication, but we have demonstrated that it is also expressed as a bona fide latent protein in primary effusion lymphoma (PEL) cells, and, coupled with its predominant ER localization, acts in an autocrine manner to support PEL growth and survival. These activities of vIL-6 are mediated not only through gp130 receptor-mediated signal transduction but also via interactions of vIL-6 with the previously uncharacterized ER membrane protein vitamin K epoxide reductase complex subunit 1 variant-2 (VKORC1v2). One effect of vIL-6 interaction with VKORC1v2 is suppression of lysosomally-localized pro-apoptotic cathepsin D (CatD) through co-interaction-mediated ER retention and degradation of ER-transiting pro-CatD. In addition, we have identified pro-replication activities of vIL-6 in PEL and endothelial cells, functions mediated through vIL-6/gp130 signaling and via vIL-6-VKORC1v2 interaction-dependent mechanisms including CatD suppression. However, the full repertoire of ER-localized vIL-6 interactions and associated activities has yet to be uncovered and appreciated. Preliminary data from co-precipitation/mass spectrometry and co-precipitation/immunoblot analyses have identified new interactions of vIL-6 and VKORC1v2 with key components of ER-associated (protein) folding (ERAF) and degradation (ERAD) pathways in addition to proteins involved in post-ER trafficking and lysosomal functions. ER stress-initiated unfolded protein response (UPR) is, in part, regulated by ERAF and ERAD and its restriction is critical for successful virus productive replication, and possibly latency as well. We hypothesize that ER-localized vIL-6 functions of relevance to HHV-8 biology include regulation of ERAF and ERAD in addition to lysosome- associated activities. This application focuses on determining the functional significance of newly-identified interaction partners of vIL-6 and vIL-6-targeted VKORC1v2 to identify novel ER-localized functions of vIL- 6/VKORC1v2 in virus biology. The project comprises: (1) physical analyses of vIL-6/VKORC1v2 interactions with ER quality control (ERAF and ERAD) and ER-transiting lysosomal and other proteins; (2) functional analyses of these vIL-6/VKORC1v2 interactions; (3) identification of the roles of the characterized interactions and activities in addition to vIL-6/gp130 signaling in HHV-8 infection and latent and lytic biology. We believe that the proposed work represents a novel and important area of research that will provide scientific impact through identification of entirely new functions of a viral cytokine and could also be of value for future development of anti-viral and therapeutic strategies.